The overall goal of this project is to identify and characterize novel molecules that may be involved in the behavioral sensitization of methamphetamine (MAP) and combined methamphetamine and alcohol-induced behavioral sensitization. The hypothesis is that combined administration of MAP and alcohol will cause greater behavioral sensitization than that produced by MAP alone, and that these changes may be correlated with changes in brain mRNA, brain proteins, or brain dopamine receptor function. The specific aims of this study are: 1. to define the behavioral effects of acute and chronic methamphetamine and concurrent methamphetamine and alcohol administration to mice 2. to identify differentially expressed mRNAs after chronic methamphetamine and combined methamphetamine and alcohol treatment 3. to characterize the single and combined drug effects of methamphetamine and alcohol on dopamine D1 and D2 binding sites and dopamine receptor mediated cAMP activity in selective brain areas.